1. Field of the Invention
The invention relates to laminating a functional film onto an injection molded ophthalmic lens using the clamp pressure and residual resin heat to bond a surface of the film according to a hot melt adhesive (HMA) function.
2. The Prior Art
In the manufacture of plastic lenses, the injection molded lens is removed from the mold for further processing. Typically the lenses are cleaned and dip-coated with a tint coating, photochromic coating, anti-reflective coating, hard coating or other protective coating layers. The cleaning and dip-coating process requires a large investment of space, resources and energy.
Other approaches involve laminating a single or multi-layer film onto the lens. One technique known as film insert molding (FIM) places the film into the empty cavity of the injection molding machine. The molten resin is then injection molded into the cavity so that the high temperature melts the facing layer of the film, causing it to fuse to the subsequently solidified lens. By way of example, this technique is described in U.S. Pat. Nos. 5,827,614, 6,328,446, 6,814,896 and 6,659,608. A serious drawback of FIM, is the requirement that the facing layer of the film be the same or compatible with the lens resin to obtain a fusion between the material of the facing layer of the film and the injected resin. Another drawback of FIM, is related to the high temperature required to obtain melted resin which could degrade or partially destroy the functionality built into the film.
Another technique to make a polarized lens uses thermal glue to adhere the film or film on to the lens. Typically a liquid glue is applied to the lens or film, while the lens is still in the mold. This approach is technically challenging because the amount of glue needs to be carefully controlled based on its viscosity and other rheological properties. Several factors can affect the thickness and the resulting optical quality. The glue can also run out and contaminate the removable inserts of the molding machine. One attempt to cure these problems, proposes to use a pressure sensitive adhesive (PSA) on the film. The PSA is relatively soft even after lamination, and may reduce the overall durability of the completed lens. By way for example this technique is described in U.S. patent application Ser. No. 2007/0195422.
Accordingly, it would be desirable to provide a simplified process for adding functional layers to a lens.